Apparatus for electrical stimulation, in particular for bruxism

Title: Apparatus for electrical stimulation, in particular for bruxism.Abstract: The present invention relates to a method and an apparatus for preventing, diagnosing, monitoring, and/or treating bruxism as well as related diseases of an individual. In a first aspect the invention relates to an apparatus for preventing bruxism of an individual, comprising: means for applying a plurality of stimulation signals for providing relaxation of at least one of the masticatory and/or facial muscles of said individual, means for applying said stimulations signals with a predefined setting, and means for applying said stimulations signals independent of activity of said muscle(s). The invention may be suitable for both nocturnal and awake bruxism. ...

The present invention relates to a method and an apparatus for preventing, diagnosing, monitoring, and/or treating bruxism as well as related diseases of an individual.

BACKGROUND OF INVENTION

Bruxism is a condition characterised by powerful jaw movements without any real function and which takes the form of involuntary grinding movements of the teeth during strong clenching. This affliction may cause serious dental damages such as for example wearing of the teeth, damage to lips and the tongue, lose teeth, and gingival pockets. Bruxism is often in addition also associated with pain in the back of the head and chronic headache.

Chronic bruxism is divided into nocturnal and awake bruxism, where the latter is also denoted daytime bruxism. Awake bruxism is characterized by being a conscious clenching of upper and lower jaws and grinding of the teeth, although dominated by the latter. Since night-time bruxism is unconscious it may normally only be perceived by those in the surroundings (for example relations) as an unpleasant squeaky noise. Awake bruxism may often be provoked by exposure to stress. It may be relieved relatively easily by drawing the attention of the person to the bruxism. Night-time bruxism is often alleviated by protecting the teeth with a splint.

SUMMARY

Attempts have been made to detect night time bruxism by the use of an electronic monitoring apparatus which provides a feedback or alarm signal when bruxism is detected. WO2004/087258 describes a sophisticated and effective form of such apparatus in which EMG (electromyography) signals are picked up from an electrode on the skin and are analysed electronically. The feedback signal is a stimulation signal sent back to the skin via the same electrodes. This signal is intended to be sufficient to have an effect on bruxism but not so strong as to wake the user.

In a first aspect, an object of the invention is to provide a more simple solution to prevent bruxism of an individual by applying a stimulation signal randomly in relation to any muscle activity. This is achieved by an apparatus for preventing bruxism of an individual, comprising:
means for applying a plurality of stimulation signals for providing relaxation of at least one of the masticatory and/or facial muscles of said individual,
means for applying said stimulations signals with a predefined setting, and
means for applying said stimulations signals independent of activity of said muscle(s).

The invention furthermore relates to a method for preventing bruxism of an individual, comprising the steps of:
applying a plurality of stimulation signals for relaxation of at least one of the masticatory and/or facial muscles of said individual,
applying said stimulations signals with a predefined setting, and applying said stimulations signals independent of activity of said muscle(s).

The invention may be suitable for both nocturnal and awake bruxism.

To prevent bruxism it is crucial to provide relaxation of the muscles involved in the bruxism. These muscles are typically one or more of the masticatory and/or facial muscles. It is most common to stimulate the masseter and/or the temporal muscle. The stimulation signal applied to a muscle is provided to obtain subsequent relaxation of that muscle. In this aspect the stimulation signals are preferably applied independent of the state of any of the implicated muscles, i.e. in this aspect the stimulus is applied independent of whether the muscle is contracting or relaxed, i.e. independent of the individual contraction event. Furthermore, the apparatus may be adapted to apply the stimulation signals in one or more predefined periods during sleep if it is known that bruxism events are most likely in said period(s), see also below for a more detailed discussion of periods. Thus, in this embodiment of the invention monitoring of muscle activity is not provided. Thereby processing of monitoring signals is not necessary and a simple solution is provided.

Preferably at least one electrode assembly is provided for attaching to the skin of the individual for applying the stimulation signals.

In a preferred embodiment of the invention a stimulation signal is a pulse train with one or more of the following parameters being predefined: start current, end current, start voltage, end voltage, pulse width, pulse train duration, inter-pulse spacing, duty cycle (pulse), pulse set spacing, duty cycle (pulse set). One or more of the parameters can be pre-set as hardware defined parameters. Preferably an administrative user, a specialist, doctor, dentist or the like can define one or more of these parameters to fit the individual user of the apparatus. Preferably the user can define one or more of these parameters based on personal preference. See also below, wherein pulse set, pulse train, interpulse spacing, duty cycle etc. are discussed in details using preferred values.

In a preferred embodiment of the invention, said predefined setting comprises at least one frequency and/or at least one intensity of the applied stimulation signals. The frequency of the stimulation signals determines how often and when the stimulation signals are applied. The intensity of the stimulation signals are preferably determined by the user, e.g. during setup of the apparatus when the user can apply the stimulation signals at a range of different intensities and observe the effect of each intensity setting. Based on the user's individual preferences, the user can select a suitable intensity.

In one embodiment of the invention the intensity of the stimulation signals is defined by a current value. Furthermore, the intensity of the stimulation signals is preferably regulated by the current, i.e. current control. And by providing a current control to the regulation of the apparatus it is ensured that each stimulation signal will be provided with the correct predefined current value, i.e. each stimulation signal is provided with the predefined intensity and the electric shock applied to the user will thereby be the same and thereby felt similar as during setup. Preferred current values are discussed below.

The predefined settings may be determined by a specialist, an administrative user, the individual user and/or the like. In another embodiment at least a part of the settings are adapted automatically during use.

There may be more than one frequency relating to the stimulation signal. E.g. the stimulation signals, or a pulse train of stimulation signals, may be applied in packets. For example a packet of stimulation signals may be applied every minute for a period of time or every 30 seconds, or every 20 seconds. The packet of stimulation signals may have an internal frequency, e.g. within a packet the stimulation signals are applied once every second for ten seconds. FIG. 3 shows a graphic presentation of pulses and packets in a period. The pulse frequency is the rate of pulses during a burst, and the burst frequency is the rate of bursts during a packet. The packet frequency is then the rate of packages during a period. The period may for example be the whole sleep period, or the periods during sleep for which it is experienced that the bruxism events are most likely to occur. FIG. 9 shows consecutive waves of non-REM-to-REM (solid horizontal boxes) sleep cycles (I to IV). During the first third of the night, slow-wave sleep (stages 3 and 4) is dominant. During the last third of the night, the REM stage is longer. (MT movement time, WT wake time) (Adapted from Lavigne et al with permission). FIG. 10 shows that the grinds per hour varies with the sleep cycles. Accordingly, a period may be the part of a sleep cycle having increased grinding events.

In one embodiment of the invention the stimulation signals, also denoted pulses, are provided randomly and/or can be provided randomly, such as randomly distributed over at least one period of time.

In one embodiment of the invention the stimulation signals over a period of time are applied with a frequency of 0.00001-100 Hz, such as 0.00001-0.0001 Hz, 0.0001-0.001 Hz, 0.001-0.01 HZ, 0.1-1 Hz, 1-5 Hz, 5-10 Hz and/or 10-100 Hz.

In one embodiment of the invention the apparatus comprises a housing and electrodes, with the electrodes preferably mounted on one side of the housing. Preferably the housing has a width and/or length which is substantially larger than the height, such as at least 2, 3, 4, 5, 6, 7 or 8 times the height. The height of the housing is the height measured perpendicular to the skin when attached to the skin of an individual.

The entire device may thus have a height of less than 20 mm, such as less than 15 mm, such as less than 12 mm, such as less than 10 mm, such as less than 8 mm, such as less than 7 mm, such as less than 6 mm, such as less than 5 mm, such as less than 4 mm, such as less than 3 mm, less than 2 mm, such as less than 1 mm. The device may be flexible to provide optimal comfort for the user.

The length of the housing may be 20 mm to 100 mm, such as 30 to 90 mm, such as 40 to 80 mm, such as 50 to 70 mm. The length of the housing covers the extension of all the electrodes.

The width of the housing may be 10 to 60 mm, such as 20 to 50 mm, such as 30 to 40 mm.

In one embodiment the housing accommodates at least one battery and the necessary electronics. The housing may also comprise an interface to e.g. a main terminal or a PC for changing the setting of the apparatus, recharging the battery and the like. Connection with a main terminal or the PC may be wireless. See also FIG. 13 and Example 6 for further details.

Combination Apparatus

In a second aspect of the invention the apparatus further comprises means for monitoring signals indicative of bruxism, means for processing of said signals in order to detect bruxism, and means for providing a feedback signal in response to detection of bruxism. Thus, this embodiment is a combination of features where stimulation signals can be provided independent of muscle activity but stimulation signals may also be provided when bruxism is detected. In this case the stimulation signals will be feedback signals, because they are applied as a result of a specific muscle activity. An example according to this aspect is a device as shown in WO2004/087258 further comprising means as defined above for providing stimulation signals independent of muscle activity.

Another aspect of the invention relates to a kit with bruxism monitoring (and/or treatment) combined with a standalone miniature device.

Adaptation to Bruxism Events

The extent of bruxism may vary greatly from person to person in terms of frequency, intensity and duration and also in terms of outcome and impact of the bruxism, e.g. diseases, pain, sufferings and malfunctions as a direct or indirect result of bruxism.

There may also be differences in how individuals experience and react to the stimulation signals, both conscious and unconscious, physically and mentally. Therefore a further aspect of the invention relates to individually adapting the stimulation signals applied to an individual based on monitored muscle activity signals. Preferably also based on how the individual adapts to the applied stimulation signals, i.e. the stimulation signals may be continuously optimised. In one embodiment of the invention the frequency and/or intensity of the applied stimulation signals are adjusted in response to intensity, impact, frequency and/or duration of detected bruxism episodes. Thus, the settings of the stimulation signals that are provided independent of muscle activity may be adapted to an actual detected bruxism pattern and/or adaptive intelligent calculations based on detected muscle activity. For example the apparatus may be self-adaptive, e.g. by means of pattern recognition, to address a bruxism event before the actual event, i.e. muscle activity may show a certain pattern before bruxism begins, and preferably the apparatus may provide recognition of said pattern and stimulate and relax the muscles before bruxism begins. There may for example prior to bruxism be an increased tension in the muscle, certain characteristic frequencies or spikes in the muscle activity signals and/or the like. In known anti-bruxism devices bio-feedback is provided when a certain muscle activity intensity threshold is reached, i.e. typically after bruxism has begun.

Treatment

A third aspect of the invention relates to a method for treatment of one or more of the following disorders: bruxism, awake bruxism, chronic bruxism, night time bruxism, dental wear, temporal mandibular joint disease (TMJ), tinnitus, migraine, headache, tension headache, preferably by means of any of the listed apparatuses.

Adaptation to Changes in Skin-Electrode Connection

A fourth aspect of the invention relates to a stimulation apparatus that adapts to changes in skin-electrode connection. The apparatus may be an apparatus applying signals independent of muscle activity or an apparatus using feedback stimulus as well as a combination apparatus as discussed above.

The stimulation signal corresponds to a mild electric shock provided to the user. A voltage is applied between two or more electrodes and the actual stimulation/shock felt by the user is determined by the amount of current transferred via the skin between the electrodes. The amount of current will depend on the connection between skin and electrodes, i.e. poor connection may result in higher resistance providing a lower flow of current for the same voltage. However, a better skin-electrode connection, possibly due to perspiration, may result in a higher flow of current and thus an increased electrical shock applied to the user.

An object of the invention is therefore to provide a muscle stimulation apparatus that adapts to changes in the skin-electrode connection. This is provided by an apparatus for providing a plurality of current controlled electrical stimulation signals to at least one of the masticatory and/or facial muscles of an individual, said apparatus comprising:
at least one electrode assembly for applying the stimulation signals to the skin of the individual,
means for defining the intensity of the stimulation signals by a current value, and
means for adapting to change in the skin-electrode contact by means of regulating the stimulation signals by the current.

The invention furthermore relates to a method for providing a plurality of current controlled electrical stimulation signals to at least one of the masticatory and/or facial muscles of an individual, said method comprising the steps of:
defining the intensity of the stimulation signals by a current value,
applying the stimulation signals to the skin of the individual by means of at least one electrode assembly, and
adapting to change in the skin-electrode contact by means of regulating the stimulation signals by the current.

By adapting to change in the conditions the stimulation signals will be more consistent and thereby more pleasant to the user (i.e. the individual). The intensity of the stimulation signals are preferably determined by the user, e.g. during setup of the apparatus when the user can apply the stimulation signals at a range of different intensities and observe the effect of the electric shock felt at each intensity setting. Based on the user\'s individual preferences, the user can select a suitable intensity. This intensity is preferably defined by a current value. And by providing a current control to the regulation of the apparatus it is ensured that each stimulation signal will be provided with the correct predefined current value, i.e. each stimulation signal is provided with the predefined intensity, and the electric shock applied to the user will thereby be the same and thereby felt similar as during setup.

If the skin-electrode conditions change during use of the apparatus the current controlled stimulation signals will provide for an automatic adaptation to the changing conditions. For example a better skin-electrode connection, i.e. lower impedance between electrodes, will provide for a lower applied voltage between the electrodes to provide for the correct current in the stimulation signal.

In a fifth aspect of the invention the apparatus comprises more than one electrode assembly. Preferably the stimulation signals to each electrode assembly are current controlled. Preferably the intensity of the stimulation signal applied to each electrode assembly can be defined independently.

In a sixth aspect of the invention the apparatus further comprises
means for providing supervisory signals indicative of muscle activity relating to bruxism of said individual by means of at least one electrode assembly,
means for processing said supervisory signals in order to detect bruxism, and
means for providing a current controlled electrical stimulation signal in response to detecting bruxism.

A seventh aspect of the invention relates to monitoring the skin-electrode contact by continuously monitoring the impedance between the electrodes in the electrode assembly by means of an embedded monitoring signal.

The current of a stimulation signal may be least 0.5 mA, such as at least 1.0 mA, such as at least 1.5 mA, such as at least 2.0 mA, such as at least 2.5 mA, such as at least 5.0 mA, such as at least 7.5 mA, such as at least 10.0 mA, such as at least 12.5 mA, such as at least 15.0 mA, such as at least 17.5 mA, such as at least 20.0 mA, such as between 0 and 7 mA, such as between 1 and 7 mA.

The apparatus according to the invention is preferably current controlled, however for practical reasons a certain degree of voltage control may be necessary. Thus in further embodiments of the invention a stimulation signal is 50-100% current controlled and 0-50% voltage controlled, such as 50% current controlled and 50% voltage controlled, such as 55% current controlled and 45% voltage controlled, such as 60% current controlled and 40% voltage controlled, such as 65% current controlled and 35% voltage controlled, such as 70% current controlled and 30% voltage controlled, such as 75% current controlled and 25% voltage controlled, such as 80% current controlled and 20% voltage controlled, such as 85% current controlled and 15% voltage controlled, such as 90% current controlled and 10% voltage controlled, such as 95% current controlled and 5% voltage controlled, such as 99% current controlled and 1% voltage controlled, such as 100% current controlled and 0% voltage controlled.

FIG. 1 is a graphic representation of the current applied during a stimulus depending on the contact resistance, ie. resistance between the skin and the electrode. The line ------shows the current applied during a 100% current controlled apparatus, whereas the line . . . shows the current applied during a 100% voltage controlled apparatus. The line ______ (Grindcare) shows the current applied when a degree of voltage control is included, in the present example the stimulation signal is about 80-90% current controlled and 10-20% voltage controlled.

In a further embodiment of the invention the electrode assembly comprises more than one electrode.

In a further aspect of the invention the at least one electrode assembly can be applied to the skin of the individual at various positions of the head, such as at or near to the following anatomical regions: temple, forehead, cheek, mandible, maxillary jaw, nose, neck, mouth, ear, and/or the like.

Monitoring Anatomical Location of Muscular Activity

An eight aspect embodiment of the invention relates to monitoring the anatomical location of muscular activity related to bruxism of an individual and comprises:

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